This invention relates to a method and apparatus for the catalytic oxidation of environmentally harmful compounds, CO and other compounds that are environmentally harmful.
Of interest are commonly owned copending U.S. applications Ser. No. 60/222,261 entitled Conversion of Nitrogen Oxides in the Presence of a Catalyst Supported on a Mesh-like Structure filed Jul. 31, 2000 in the name of Joakim A. Carlborg et al., Ser. No. 60/159,800 entitled Conversion of Nitrogen Oxides in the Presence of a Catalyst Supported on a Mesh-like Structure filed Oct. 15, 1999 in the name of Joakim A. Carlborg et al., Ser. No. 09/181,186 entitled Method and Apparatus for Making a Catalyst Carrier Device Element filed Oct. 28, 1998 in the name of Vogt et al. and corresponding to PCT/US99/24907 filed Oct. 21, 1999; Ser. No. 09/265,164 entitled Exhaust Gas Catalytic Converter filed Mar. 9, 1999 in the name of J. Lloyd et al. and corresponding to PCT/US00/06137 filed Mar. 8, 2000; Ser. No. 09/156,023 entitled Coated Products filed Sep. 17, 1998 in the name of L. Schuh et al. and corresponding to PCT/US98/198111 filed Sep. 23, 1998; Ser. No. 09/589,817 entitled Heat Exchanger/Reactor Apparatus filed Jun. 7, 2000 in the name of Timothy Griffin et al., Ser. No. 09/322,524 entitled Structured Packing and Element Therefor filed May 28, 1999 in the name of Rudolf A. Overbeek et al. and corresponding to PCT/US99/10784 filed May 14, 1999; Ser. No. 09/002,539 entitled Structured Packing and Element Therefor filed Jan. 2, 1998 in the name of Bettina Paikert et al. corresponding to PCT/US98/27699 filed Dec. 29, 1998 all incorporated by reference herein in their entirety.
Emissions of environmentally harmful compounds, such as volatile organic compounds (VOC) are pollutants that are found in a large variety of environments. For example, such compounds may be found in painting and coating facilities, industrial and domestic kitchen broilers and stoves in the form of emitted smoke, the combustion products of stationary diesel and gasoline engines, processed wood products, printing facilities, and numerous other large and small scale industrial applications. In the semiconductor industry, for example, such compounds are found in isopropanol and decomposition of photoresists among others, in wood manufacturing such products are found in formaldehyde, terpenes and pinenes, in paper processing, alcohols, resin monomers and organic phosphates are present, in phthalic/maleic anhydride manufacturing, organic acids such as phthalic, maleic and benzoic need to be dealt with, in the petroleum industry gasoline vapor is present and in dry cleaning processes halogenated alkanes are involved. Thus volatile organic compounds are undesired by-products found in the above and other facilities and pollute the atmosphere including affecting atmospheric ozone. In addition, as part of the above processes, other compounds such as CO, hydrocarbons and other environmentally harmful compounds are emitted.
U.S. Pat. No. 5,643,545 incorporated by reference herein provides a more general definition of volatile organic compounds. Methods for the catalytic oxidation of organic compounds are well known and various prior art relating to this subject matter are described in the aforementioned U.S. Pat. No. 5,643,545. This patent describes VOCs as compounds with sufficiently high vapor pressure to exist as a vapor in ambient air and which react in the atmosphere with nitrogen oxides in the presence of heat and sunlight to form ozone, and include both halogenated and non-halogenated volatile organic compounds.
U.S. Pat. No. 4,416,800 discloses a method for producing a catalytic material. The support material has the shape of a fibrous sheet consisting of non-metallic inorganic fibers mixed with a catalyst carrier powder. The product can be further treated by impregnation in slurry or solution containing carrier materials and catalytically active agents. The catalytic material can be used for:
a) reduction of nitrogen oxides in the presence of ammonia (catalyst: Cu, Fe, V, W and Mo on Al2O3 or TiO2)
b) oxidation of carbon monoxide and hydrocarbons (catalyst: Pt on Al2O3 or TiO2)
Other US Patents of interest relating to reactors and catalytic converters including metal-ceramic combusters, converters for treating gases to remove pollutants, ordered catalyst bed packings, catalyst supports and fluid treatment devices and fixed bed reactors, include U.S. Pat. Nos. 5,026,273, 4,942,020, 4,471,014,4,330,436, 3,949,109, and in addition, U.S. Pat. No. 5,653,949 (oxidation catalyst for controlling VOC), U.S. Pat. No. 5,650,128 (method of destruction of VOC flows of varying concentration), U.S. Pat. No. 5,478,530 (hot mix asphalt plant with catalytic reactor), and U.S. Pat. No. 5,375,562 (catalytic incineration system).
A process for removing environmentally harmful compounds from a fluid, in particular a gas, according to the present invention comprises forming a substrate comprising a randomly oriented mesh-like fibrous porous material having opposing sides, the material for promoting contact between fluids flowing over the surfaces of the material at the opposing sides, the material having pores exhibiting a range of sizes from sub-micron to no greater than about 500 microns, the pores having a plurality of interstices in communication with each other and externally the material, the material being arranged to create turbulence in the fluid flowing adjacent to the sides which turbulence creates a pressure differential across the material for promoting the flow of the flowing fluid from one side to the other side through the pores and interstices essentially over the entire surface of the material; and oxidizing the environmentally harmful compounds in the fluid in the presence of an oxidizing catalyst supported on the material, the catalyzed mesh-like structure having a porosity of greater than about 65%.
An apparatus for removing environmentally harmful compounds from a fluid flowing into the apparatus in a given direction in accordance with a further aspect of the present invention comprises a packing structure formed of a ceramic fibrous mesh-like porous structure having a porosity of greater than about 85% and having opposing sides, the material having pores exhibiting a range of sizes from sub-micron to no greater than about 500 microns, the pores forming a plurality of interstices in communication with each other and externally the material, the material being arranged to create turbulence in the fluid flowing at the sides which turbulence creates a pressure differential across the material for promoting the flow of the flowing fluid from one side to the other side through the pores and interstices essentially over the entire surface of the material for promoting contact between fluids flowing over the surfaces of the material at the opposing sides; and including a catalyst coated on the packing structure for oxidizing the environmentally harmful compounds in the fluid in contact with and flowing through the pores of the structure.
In a further aspect the mesh-like structure has a porosity of greater than 90%.
In a still further aspect, the environmentally harmful compounds are volatile organic compounds (VOC) including hydrocarbons, CO and any other constituent that participates in atmospheric photochemical reactions to produce for example ozone or smog constituents, combustible compounds to be removed from a gas stream for reasons of toxicity, photochemical reactivity or physical discomfort such as irritants, particulates, odor sources, compounds which may cause upper atmosphere ozone depletion or lower atmosphere ozone formation and any organic compound which participates in atmospheric photochemical reactions excluding carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate.
In a further aspect, the mesh-like structure or packing material is formed of fibers made of metal or ceramic.
In a further aspect, the catalyst is coated on the mesh-like structure and preferably the coating thickness is less than 30 microns.
In a further aspect, the environmentally harmful compounds are any compound of carbon, excluding carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participate in atmospheric photochemical reactions.
Preferably the packing structure comprises corrugated sheets each having a plurality of parallel corrugations, the corrugations of adjacent sheets being oriented at an angle relative to the given flow direction.
In a further aspect, the packing structure comprises adjacent corrugated sheets., each sheet with parallel corrugations, the corrugations of adjacent sheets at a respective angle xcex1, xcex1xe2x80x2 to the given direction.
Preferably the angle xcex1, xcex1xe2x80x2 is in the range of about 30xc2x0 to about 80xc2x0.